The primary objective of this study is to establish the dose-response relationship with regard to efficacy and safety of BIBR 1048 (50 mg bis in die(b.i.d), 150 mg b.i.d, 225 mg b.i.d. and 300 mg quaque die(q.d) ) in preventing venous thromboembolism(VTE) in patients undergoing primary elective total hip and knee replacement.